Photocurrent Enhancement by Spontaneous Formation of a p–n Junction in Calcium‐Doped Bismuth Vanadate Photoelectrodes

Abstract The application of bismuth vanadate (BiVO 4 ) photoelectrodes for solar water splitting is hindered by the poor carrier transport. To overcome this, multiple donor‐doping strategies (e.g. dual doping, gradient doping) have been explored. Here, we show for the first time the successful introduction of calcium (Ca) as an acceptor‐type dopant into BiVO 4 photoelectrodes. Interestingly, instead of generating cathodic photocurrents, the Ca‐doped BiVO 4 photoelectrodes show anodic photocurrents with an enhanced carrier separation efficiency. Hard X‐ray photoelectron spectroscopy (HAXPES) shows that this enhancement is caused by out‐diffusion of Ca during the deposition process, which spontaneously creates a p–n junction within the BiVO 4 layer. Overall, a significant two‐fold improvement of the AM1.5 photocurrent is obtained upon Ca‐doping. This study highlights the importance of controlled doping beyond simply modifying carrier concentration and may enable new device architectures in photoelectrode materials.